My recently acquired A3 SE TDI auto sometimes suffers erratic tick over when Drive is engaged causing jerky take off. The Audi dealer could find no errors showing on the diagnostic tester, and even suggested it was inherent in the model. Anybody else had the same problem? Could it be a faulty torque converter, even though gear changes are imperceptible? Is there an anti-stall control or idle valve that might be faulty?